Trisilanol polyhedral oligomeric silsesquioxane (POSS) are a category of inorganic-organic material that comprise an inorganic open cage silica structure, organic attachments, and silanol ( - Si - OH) groups. Recently, trisilanol POSS was added to Al-based alloys, and found to promote substantial microstructural refinement, and improved mechanical strength and fatigue life compared to conventional compositions. Such microstructural modifications and property enhancements are usually attributed to silanol - Al bonds that formed within the liquid-state, prior to solidification. However, details of such high-temperature chemical interactions remain unclear. Here, we performed ab initio molecular dynamics simulations at 1500 K, to probe the chemical interactions between isolated trisilanol POSS molecule and discreet Al atoms. Al atoms modified the silanol groups to form, two energetically favorable coordinate complexes: monodentate - Si - O - Al and bidentate - (Si - O) 2 - Al. Such complexes were formed by Al atoms attracting electrons towards themselves from the POSS molecule. Crucially, this bonding mechanism allowed trisilanol POSS to organize the neighboring Al atoms into geometric motifs that can potentially serve as nucleation sites within liquid-Al, and facilitate microstructural refinement.

Hydrosilylation of double-decker silsesquioxanes is an efficient approach for preparing hybrid materials, especially polymeric materials. Karstedt's catalyst, Pt(dvs), is widely used for this purpose due to its commercial availability, high yields, and good hydrosilylation selectivity. Despite this, vinylbenzenes have been shown to produce multiple hydrosilylated products. This study employs a method involving an iridium catalyst that was significantly more selective for the anti-Markovnikov hydrosilylation product with vinylbenzenes and bis-silane-capped double-decker silsesquioxanes. Obtaining higher purity of hydrosilylated products will allow for the development of the fundamental structure-property relationship of hybrid materials.

Atmospheric plasma processing, which combines the efficacy of chemical processes and the safety of physical processes, has been used to modify the surface characteristics of graphite-based materials. In this work, two distinct plasma source gases, C4F8 and O2, with the addition of a rotary reactor were used. The effectiveness of modifying the basal plane of intercalated graphite nanoplatelets (GnP) was investigated with various analytical techniques and the visual observation of the dispersion of these plasma-treated GnP in solvents was also reported. It is shown that this low-temperature plasma processing technique can be used to successfully modify the GnP surface without significantly changing the intrinsic structure of the GnP, which is desirable in many applications. With the C4F8 plasma treatment, the immersion characteristics in solvents can be tuned and the functional groups present on the surface can be tailored to produce desired bonding environments. This surface chemistry tunability will provide the needed functionalities in creating graphene-containing composite materials.

The relaxation dynamics of polystyrene (PS)/silica nanocomposites after a large step deformation are studied by a combination of small-angle scattering techniques and rheology. Small-angle X-ray scattering measurements and rheology show clear signatures of nanoparticle aggregation that enhances the mechanical properties of the polymer nanocomposites (PNCs) in the linear viscoelastic regime and during the initial phase of stress relaxation along with accelerated relaxation dynamics. Small-angle neutron scattering experiments under the zero-average-contrast condition reveal, however, smaller structural anisotropy in the PNCs than that in the neat polymer matrix, as well as accelerated anisotropy relaxation. In addition, the degrees of anisotropy reduction and relaxation dynamics acceleration increase with increasing nanoparticle loading. These results are in sharp contrast to the prevailing viewpoint of enhanced molecular deformation as the main mechanism for the mechanical enhancement in PNCs. Furthermore, the observed acceleration of stress relaxation and reduction in structural anisotropy point to two types of nonlinear effects in the relaxation dynamics of PNCs at large deformation.

Bisfunctional dichlorosilanes were reacted with tetrasilanol of double-decker shaped octaphenylsilsesquioxane (DDSQ) to form fully condensed DDSQ compounds. The crystallographic and thermal characteristics of these compounds were examined. For compounds capped with dichlorosilanes bearing linear aliphatic moieties, as the number of carbon increases from methyl to n -butyl (from 1 to 4) the melting temperature, T m , dropped from 546 K to 416 K. While for compounds capped with cycloaliphatic, as the moiety changes from cyclopentyl to cyclohexyl, the value of T m increases from 533 K to 555 K. Surprising, the highest T m observed was that when capping was done using diisopropyl dichlorosilane. A T m of around 565 K was observed, which was even higher as compare to diphenyl dichlorosilane capped DDSQ, which had T m of about 526 K. Phase behavior of binary and ternary mixtures of these condensed DDSQ was also investigated. To our surprise, mixtures of these compounds form eutectic. The eutectic points were calculated based on ideal binary and ternary eutectic from the thermal properties of pure components. Depending on the crystallography, experimental observations of eutectic match well with calculated values.

Corrosion-induced failure along the Cu and Cu9Al4 interface is a major reliability concern for the Cu-wire-bonded packages. The open circuit potential, Eoc, and the corrosion current density, icorr, of Cu and Cu9Al4 with varying amounts of Pd addition were characterized using the potentiodynamic polarization method at 25 degrees C, 45 degrees C, and 65 degrees C. At a given temperature, Pd addition to Cu caused the value of Eoc to increase and the value of icorr to decrease due to the higher nobility of Pd. For the Cu9Al4 intermetallics, although Pd addition caused an increase in the value of Eoc attributed to the high nobility of Pd, the value of icorr increases with small amounts of Pd addition due to high cathodic activity of Pd. To further evaluate the effect of Pd addition in preventing the corrosion of Cu wire bonds, galvanic current densities, ig, between Cu and Cu9Al4 and their Pd-doped couples were also measured. At 25 degrees C and 45 degrees C, the stabilized value of ig decreases with an increasing amount of Pd addition. At 65 degrees C, the stabilized value of ig was not lower until 9 wt.% Pd was added. The results of both self- corrosion and galvanic corrosion suggest that the amount of Pd needs to be above a critical value to effectively prevent Cu wire corrosion regardless of the operating temperature.

Trisilanol phenyl polyhedral silsesquioxane (phenyl TSP) was added to a commercial aluminum alloy, AlSi10MnMg, to investigate its influence on microstructure, mechanical properties, and solidification behavior. Addition of phenyl TSP was successful in refining the morphology of the eutectic Si into an ultrafine lamellar structure. Furthermore, this refined as-cast morphology can be obtained even when the molten aluminum alloy was held for 96 h in a furnace set at around 1000 K. This no fading phenomenon is of a significant processing benefit to the current use of Sr for refining the eutectic morphology. The ductility of phenyl TSP-refined AlSi10MnMg alloy was consistent with Sr-modified alloy at room, 423 K, and 573 K elevated temperature while maintaining similar strength. Cooling curve analysis showed the Al–Si eutectic arrest temperatures during solidification were decreased with the phenyl TSP addition, suggesting phenyl TSP bonds with Al to slow down the Al segregation from Al–Si melt during the eutectic reaction, leading to the microstructural refinement of Al–Si eutectic.

Architecture and microstructure of type I collagen fibers constitute central regulators of tumor invasion with aligned fibers providing a route for migration of stromal and cancer cells. Several different aspects of fibrillar collagen, such as stiffness, density, thickness, and pore size, may regulate migration of cancer cells, but determining effects of any one parameter requires clear decoupling of physical properties of collagen networks. The objective of this work is to develop and apply an in vitro three-dimensional (3D) tumor-extra cellular matrix (ECM) model with tunable physical parameters to define how stromal fibroblasts modulate collagen microstructure to control migration of breast cancer cells. We incorporated two different types of polyhedral oligomeric silsesquioxane (POSS) nano-molecules into a collagen/alginate matrix to induce different mechanisms of gelling. The resultant biomimetic, nanocomposite hydrogels show different collagen fibrillar microstructures while maintaining constant overall matrix stiffness, density, and porosimetry. Spheroids of human mammary fibroblasts embedded in these 3D matrices remodel the collagen network to varying extents based on differences in underlying matrix microstructures. The remodeled collagen matrix shows oriented, thicker fibrillar tracks, facilitating invasion of tumor cells. By decoupling effects of matrix stiffness and architecture, our nanocomposite hydrogels serve as robust platforms to investigate how biophysical properties of tumor environments control key processes regulating tumor progression in breast cancer and other malignancies. STATEMENT OF SIGNIFICANCE: Our manuscript demonstrates a new type of nanocomposite hydrogel with two different gelling mechanisms, produced by incorporating two types of polyhedral oligomeric silsesquioxane (POSS) nano-molecules into a collagen/alginate matrix. The resultant biomimetic hydrogels show different fibrillar collagen microstructures while maintaining constant overall matrix stiffness, density, and porosimetry. These gels allow us to uncouple effects of matrix stiffness versus architecture on migration and invasion of breast cancer cells and stromal fibroblasts. Upon embedding spheroids of human mammary fibroblasts (HMFs) and dissociated 231 breast cancer cells, we showed that HMFs remodeled the collagen network to differing extents dependent on starting matrix microstructures in each hydrogel. The remodeled collagen matrix showed aligned collagen fibers perpendicular to the surface of a spheroid with migrating HMFs following these fibers as occurs in tumors in vivo. To our knowledge, this is the first study showing significant different fibrillar collagen microstructures with constant collagen density and gel stiffness. This study establishes a new type of nanocomposite 3D hydrogels for studies of biophysical and cellular interactions in engineered tumor environments.

A strategically novel synthesis of nano-sized, asymmetrically functionalized double-decker shaped silsesquioxanes (DDSQ) is reported. Selective protection with a boronic acid affords the crucial mono-protected intermediate en route to the asymmetric products. Generation of symmetric by-products is minimized by judicious choice of base, and high recovery of recyclable starting DDSQ tetraol is achieved.

The ball-bond interface between Cu wire and Al pad is a layered structure consisting of Cu, Cu9Al4, CuAl2, and Al. Bond failure often occurs between the Cu9Al4-CuAl2 layer due to the high galvanic corrosion rate and high concentration of interfacial voids. Pd-coated Cu wire and molding compound with low chloride concentration are two common practices used to enhance the bond reliability. However, the mitigating mechanisms of these two methods have not been fully revealed. In this study, electrochemical techniques including zero-resistance ammetry and polarization were used to characterize the effect of Pd addition and chloride concentration on the bond corrosion and failure behavior. Results show adding Pd and reducing chloride concentration reduced the galvanic corrosion rate between Cu and Cu9Al4. Moreover, the galvanic effect disappeared completely with a high amount of Pd addition such as 9 wt% in an electrolyte with a low chloride concentration such as 1 ppm NaCl. By reducing the chloride concentration, the galvanic corrosion rate between Cu9Al4 and CuAl2 was reduced due to a lower anodic dissolution rate of CuAl2. However, Pd addition increases the galvanic corrosion rate between Cu9Al4 and CuAl2 due to a higher cathodic activity of Cu9Al4. But, Pd is known to reduce the intermetallic growth rate and the associated internal stress buildup. Therefore, the concentration of voids at the Cu9Al4-CuAl2 interface was reduced and lead to lower bond failure rate.

Closed double-decker shaped silsesquioxanes (DDSQ(Ph)(8)-2((Me)(R))) with R as phenyl, Para-phenyl amine, and para-phenylethynyl phenyl were synthesized. Isolation of nearly pure trans and cis isomers was obtained by fractional recrystallization. Crystallographic and thermal characteristics of these isolated isomers were obtained by X-ray diffraction of a single crystal and differential scanning calorimetry (DSC). It was observed that melting temperature increases as the size of the R group decreases from para-phenylethynyl phenyl to phenyl and the magnitude of the entropy difference at melting increases as the size of the R group increases. Isolated isomers were then mixed to different cis-to-trans ratios, and their thermal characteristics investigated by DSC. The upper portion of the phase diagram was constructed for these DDSQ compounds using results from DSC traces. Interestingly, cis and trans isomers of these DDSQcompounds form a binary eutectic. Experimentally observed eutectic composition and temperature were found to be close to the calculated values based on the ideal eutectic mixing rule. These data allow users to broaden the thermal processability window by reducing the system melting temperature without affecting the reaction onset temperature of the functional groups.

By virtue of regio-and geometric isomers, functionalized double-decker silsesquioxanes (DDSQ) may offer unique access to silsesquioxane-based hybrid materials with multifaceted performance characteristics.Analytical methods were as used to separate cis and trans isomers of various DDSQ with polar as well as nonpolar moieties.Solubility was fitted to the Schröder-van Laar equation with activity coefficients determined using the NRTL model by adjusting binary interaction parameters.For a given DDSQ compound, the variances in solubility between cis and trans isomers depend on differences in thermal properties.cis and trans isomers binary phase diagrams of DDSQs were also developed to examine the influence of the regioisomer (meta-or para-) and the nonactive organic moiety coupled on the D-silicon.DDSQ compounds with a methyl moiety exhibited eutectic phase diagrams.Their trans isomers were higher melting and exhibited larger packing density.Cyclohexyl DDSQ exhibited an isomorphic phase diagram, attributed to cyclohexyl being more similar in size to the phenyl moieties.Changing from para-to meta-aminophenyl shifted the solid-liquid equilibrium further from ideal, with decreased activity coefficients.

HPLC was used as the quantitative analysis technique in determining the molar ratio of cis and trans isomers in the double-decker shaped silsesquioxanes (DDSQ). Different experiments were performed to analyze the effects in the retention times of the polarity of moieties bonded to the DDSQ, as well as other possible adsorption driving forces. As expected, the use of adsorption HPLC was successful in separating cis and trans DDSQ isomers with the resolution of elution better than 1.5. Interestingly, the molecular size of moiety attached to the DDSQ resulted in significant reduction of the retention time suggesting the sterics constraint plays a critical role in the separation of these cage-like structures along with the strength of hydrogen bonding. In partition HPLC using Si bonded with CN groups as a normal phase resulted in a partial separation for one of the selected systems, which indicates the extent of polarity plays a secondary role in the separation mechanism.

Analytical separation parameters of a side-capped octaphenyl double-decker shaped silsesquioxanes (DDSQ) mixture with zero, one, and two hydroxyl groups were obtained with HPLC. These parameters were extrapolated for a large scale preparative separation. The frontal analysis was experimentally performed for each component in the mixture to obtain linear adsorption isotherm parameters. The slopes of the linear isotherms were related with the experimental HPLC retention times in a linear function to predict separation for other mixtures with similar characteristics. The HPLC chromatograms were simulated in ASPEN chromatography with acceptable accuracy. Parameters of the scale-up separation were determined and prediction of collection times for each compound in three different mixtures was evaluated by separations using 5 g scale. Most importantly, scale-up isolation of chemically asymmetric DDSQ structure was demonstrated.

A synthetic path to asymmetric side-capped double-decker shaped silsesquioxanes (DDSQ) and subsequent isolation is described. By strategically using a combination of dichloro and trichlorosilane capping agents, a resultant product with mixed silanol functionalities was obtained. The use of preparatory liquid chromatography (LC) cleanly separated DDSQ compound with asymmetric functionality, and HPLC provided a quantitative technique to analyze mixture ratios. These mixture ratios did not follow the expected statistical trend due to the steric effects on the rate of capping. As a consequence, a decreased amount of the desired asymmetric DDSQ was observed in some cases. This was overcome by varying the ratio of capping agents. Overall, this work demonstrates access to asymmetric DDSQ cages is feasible, and LC is an effective separation technique.

Thermosetting polyimides terminated with phenylethynly phthalic imides are the current state-of-the-art high temperature resin for use in structural composite applications. However, due to the presence of imide group these resins often suffer high moisture uptake leading to property degradation during use. In addition, the need to remove condensation near the crosslinking reaction temperature as well as high glass transition temperature of unreacted oligomers, the processing window for this class of thermosetting is very narrow. Hence, the need to develop compounds with the same terminating group with ease of processing is of significant interest. In this work, double-decker shaped silsesquioxane (DDSQ) terminated with multiple phenylethynyl groups was developed and curing process investigated. It was anticipated that DDSQ as the backbone can provide the needed monodispersed characteristics in its molecular weight, while phenylethynyl groups form different isomers (region- and stereo-) about the SiO core of DDSQ. This approach provides ease of processing while eliminate crystallinity. In addition, the inorganic nature of these compounds also exhibited a significant reduction in the moisture uptake which can greatly enhance in-service performance of composites. Synthesis and purification of needed chlorosilanes and the subsequence separation of these functionalized DDSQs by liquid chromatography were performed without the need to use fractional crystallization as the first preparation step are presented. This approach greatly reduces the complexity and enables continuous process.

The disappearance of Cu9Al4 has been observed at the failed Cu-Al ball–bond interface in the standard humidity reliability test. Galvanic corrosion has been considered as the cause of the bond failure, yet no convincing argument has been provided to explain the preferential attack on Cu9Al4. Due to encapsulation, corrosion should proceed with the thin-layer electrolyte condition. The high ohmic resistance may constrain the galvanic corrosion between adjacent entities only. Thus, in this study, the galvanic corrosion between Cu and Cu9Al4, Cu9Al4 and CuAl2, and CuAl2 and Al were investigated using the zero-resistance ammetry. The results showed that the galvanic corrosion rate was the highest for the Cu9Al4-CuAl2 couple as compared with the other two galvanic couples. Also, the observed residual alumina between Cu9Al4 and CuAl2 and the associated internal stress build-up during the CuAl2-to-Cu9Al4 transition contributed to a higher crack propagation rate. Therefore, the failure first occurs at this interface. This failure then leads to a separation of Cu and Cu9Al4 from CuAl2 and Al. For the Cu-Cu9Al4 couple, Cu9Al4, the anode should corrode significantly faster due to the strong galvanic effect imposed by a larger surface area of Cu. In contrast, for the CuAl2-Al couple, the anodic corrosion rate of Al is slow as the galvanic effect imposed by the CuAl2 cathode is weak due to the small cathode surface area. As a result, Cu9Al4 disappeared from the failed ball–bond interface.

The incorporation of cage-like silsesquioxanes (SQ) to form polymers has demonstrated property enhancements in areas such as: thermal and mechanical characteristics, flame retardance, dielectric properties, and oxidative resistance. However, with most of hybrids investigated, the attached SQs are pendant with respect to the reaction site, thus mechanical performance did not take full advantage about the rigid nature of SQ core. A recently developed class of these nano-structured, cage-like silsesquioxanes, formally known as double decker silsesquioxanes (DDSQ), offers the opportunity to form hybrids with the SQ cage as the bridge between multiple reaction sites. This advancement provided a unique opportunity to form networks with Si-O core connecting those reaction junctions, which may positively affect the mechanical performance on thermosetting polymers. It was discovered during the capping reaction, these functionalized DDSQs generate cis and trans isomers with respect to the 3D Si-O core. In addition meta- and para- functional groups may be used to form hybrid reacting monomer mixture containing six different isomers. Depending on the relative ratio of isomers in the mixture, viscosity can be well controlled with no effect on the reaction mechanism and kinetics. Therefore, it is expect to improve the processing of high temperature oligoimide resins while improve thermoxidative stability (TOS) of organic networks. Synthesis details, different methods of incorporating DDSQ mixtures and their TOS performance were presented.

This study investigated the electrochemical characterizations in the field of wire metallurgy (Pd concentration) and molding compound chemistry (chloride concentration) to find ways to reduce metallic entities' susceptibility to corrosion at ball-pad interfaces. The open circuit potentials and potentiodynamic polarization curves of various metallic entities found in a Cu(Pd)-Al bonding interface were obtained in near-neutral electrolytes of 100ppm, 20ppm, and 1ppm of NaCl in high-purity water. From X-ray diffraction spectra, it was found that Pd could be homogeneously incorporated into Cu9Al4, the Cu-rich intermetallic compound (IMC) also referred to as γ but not into CuAl2, the Al-rich IMC also referred to as θ for arc-melted specimens. For Cu-Pd alloys, at a given chloride concentration, increasing Pd concentration causes the value of open-circuit potential (Eoc) to increase and corrosion current density (icorr) to decrease. Likewise, for a given amount of Pd in Cu-Pd alloy, decrease in the NaCl concentration causes the value of Eoc to increase and icorr to decrease. Interestingly, for high concentration of Pd as in the case of Cu-9Pd, Eoc and icorr became less sensitive to the NaCl concentrations investigated. This can be attributed to the Pd enrichment on the corroding surface that reduces the anodic dissolution rate of Cu. For Pd-doped γ intermetallics, increasing Pd concentration causes a systemic increase in the value of Eoc, but at a lower concentration of Pd, the value of icorr was increased. The addition of Pd to γ causes an increase in the cathodic current density due to the high cathodic activity of Pd, while the passivation of Al in γ reduces the extent of the anodic current density reduction due to the addition of Pd, which leads to a higher value of icorr at a low Pd concentration. This is true even when the NaCl concentration is as low as 1ppm. On the other hand, the influence of NaCl concentration on the Eoc and icorr of γ IMC was always observed, even with Pd addition.